The present invention relates generally to the recovery of subterranean deposits, and more particularly to a method and system for accessing subterranean deposits from the surface.
Subterranean deposits of coal typically contain substantial quantities of entrained methane gas. There are many uses for methane gas extracted from the subterranean deposits. Substantial obstacles, however, have frustrated more extensive development and use of methane gas deposits in coal seams. A common problem in producing methane gas from coal seams may be vertical separation of multiple thin layers of coal within a coal seam. Although coal seams may extend over large areas of up to several thousand acres, the depth of the multiple layers in the coal seam may vary from very shallow to very deep. Vertical wells drilled into the coal deposits for obtaining methane gas can only drain a fairly small radius around the coal deposits. Further, coal deposits are not amenable to pressure fracturing and other methods often used for increasing gas production from conventional rock formations. As a result, production of gas may be limited in volume. Additionally, coal seams are often associated with subterranean water, which must be drained from the coal seam in order to produce the methane.
The present invention provides an improved method and system for accessing subterranean deposits from the surface that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, the present invention provides an articulated well with a drainage pattern that provides access to a large subterranean area from the surface.
In accordance with one embodiment of the present invention, a subterranean drainage pattern for accessing a subterranean zone includes a main well bore extending from a surface well bore, located at a first end of the area, to a second end of the area. A first plurality of lateral well bores extend in spaced apart relation to each other from the main well bore to the periphery of the area on a first side portion of the main well bore. A second plurality of lateral well bores extend in spaced apart relation to each other from the main well bore to a periphery of the area on a second, opposite side portion of the main well bore. A first plurality of ramping well bores extend in spaced apart relation to each other from the main well bore toward a boundary of the subterranean zone.
Embodiments of the present invention may have some, all, or none of the following advantages. In particular embodiments, an improved multi-plane drainage pattern may include upwardly ramping well bores and/or downwardly ramping well bores to maximize access to a subterranean zone. Upwardly ramping well bores may extend upwardly from the main well bore to maximize access to the upper portion of a single, thick layer of subterranean deposits. Alternatively or additionally, upwardly ramping well bores may extend upwardly from the main well bore to maximize access to multiple layers of subterranean deposits. Similarly, downwardly ramping well bores may extend downwardly from the main well bore to maximize access to a lower portion of a single, thick layer of subterranean deposits and/or to maximize access to multiple layers of subterranean deposits separated by impermeable or substantially impermeable material. In particular embodiments, multi-plane drainage pattern may include lateral well bores in addition to upwardly ramping well bores. Lateral well bores may extend from opposite sides of the main well bore in a substantially horizontal plane to provide greater access to an area of the subterranean zone. A further technical advantage may include maximizing the area covered by the drainage pattern both horizontally and vertically while reducing the number of times a drill string changes direction while drilling a bore hole. Consequently, disadvantages arising from differences in pressure head caused by vertical curves in a well bore may be substantially reduced.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the figures, description, and claims, included herein.